A two-stage supercharging system (multi-stage supercharging apparatus) has been known as a system which efficiently recovers the exhaust energy of an engine. In the two-stage supercharging system, generally, a high-pressure stage turbine of a high-pressure stage turbocharger (a first supercharger) and a low-pressure stage turbine of a low-pressure stage turbocharger (a second supercharger) are arranged in series from an upstream side of an exhaust gas flowing in an exhaust passage. Further, a low-pressure stage compressor of a low-pressure stage turbocharger and a high-pressure stage compressor of a high-pressure stage turbocharger are arranged in series from an upstream side of an intake air flowing in an intake passage. Moreover, the two-stage supercharging system is configured so as to be capable of supercharging by rotationally driving the high-pressure stage turbine and the low-pressure stage turbine using the exhaust gas of the engine and additionally compressing the intake air compressed by the low-pressure stage compressor by the high-pressure stage compressor.
For example, Patent Document 1 discloses a multi-stage supercharging apparatus including a high-pressure stage supercharger and a low-pressure stage supercharger, in which an intake passage and an intercooler are integrally formed in order to minimize the entire apparatus.